1. Technical Field
This invention relates generally to a well tool such as retrievable packer which includes a slip mechanism adapted to anchor the tool within a well. In particular, the invention relates to an improvement in the slip mechanism to allow the well tool to be moved from its anchored location in the well.
2. Background Information
In one prior art arrangement disclosed in U.S. Pat. No. 3,356,141, upper and lower sets of slip assemblies are utilized to secure a packer in a selected location in a well. Specifically, a packer sealing element is located between the upper and lower sets of slips and is compressed to expand outwardly sealing against the inside wall of a well casing as the individual slips of each assembly are set. In setting the slips, upper and lower cone assemblies respectfully engage the individual slips wedging them outwardly as the cone assemblies are forced beneath the slips. During movement of the well tool in the casing, the upper and lower sets of slips are kept from being set by a J-slot latching mechanism which maintains a specified distance between the upper and lower sets of slips. To set the slips, the J-slot latching mechanism is released by manipulation of the tubing string. Then the lower cone is freed to slide beneath the lower set of slips as the tubing string carrying the tool is pushed downwardly in the well. This wedges the slips in the lower set outwardly and into anchoring engagement with the inside surface of the well casing. As the lower set of slips bite into the well casing, any further downward movement of the tool in the well is prevented and the sealing element of the packer is compressed expanding radially outwardly to seal against the casing. Concurrently, the upper cone is wedged beneath the upper set of slips forcing each of the slips in the upper set radially outwardly to anchor in the inside wall of the casing so that the packer is held against movement either upwardly or downwardly within the well.
In order for the upper set of slips to be wedged outwardly and into the casing, the slips are carried individually within a housing which in turn is slidably mounted on a mandrel. Specifically, each of the upper slips is connected to the housing by way of a neck portion and at the upper end of the neck portion, each of the slips includes a circumferentially extending T-shaped shoulder. The latter extends in opposite directions over forked arms of the housing and supports the slip loosely on the housing with a gripping segment of each slip depending freely from the underside of the housing.
To move the tool within the well, an abutment is carried on the mandrel and when the tubing string is pulled upwardly the mandrel abutment engages the housing pulling the housing upwardly. In turn, the forked arms of the housing act against the T-shaped shoulders of the slips sliding each of the slips in an unwedging direction relative to the cone and away from anchoring against the inside wall of the casing.
To facilitate releasing the slips from the casing, the neck portion of an initial released one of the slips is shorter than the others. As a result, initial movement of the housing when lifted by the abutment causes the slip lifting forces to be concentrated on the shorter neck slip freeing the shorter neck slip before the others.
With slip releasing mechanisms of the forgoing described type, problems have been encountered in the past when the yield strength of the neck portion of any of the slips is exceeded without the slip being released. Once the neck on a slip breaks, then the slip may become jammed between the cone and the casing making it virtually impossible to remove the packer from the casing even to the extent it may become necessary the drill the jammed packer out of the well.